The goal of the project is to molecularly clone and characterize novel chemokine receptors in lymphocytes. Chemokines are members of a family of more than twenty human cytokines whose best described activities are as chemotactic factors for leukocytes. Our laboratory has focused on chemokines that specifically target activated lymphocytes. As part of studies of the actions of chemokines on lymphocyte physiology, we have screened lines of human tumor infiltrating lymphocytes (TIL) to identify novel chemokine receptors. Using the polymerse chain reaction with pools of degenerate primers we have identified two novel seven transmembrane domain receptors designated X2 and C3 that are related by sequence homology to the known chemokine receptors, and related more closely to the CXC chemokine receptors than to the CC chemokine receptors. cDNA clones isolated from libraries prepared from the TIL predict that X2 and C3 encode proteins of 374 and 342 amino acids respectively. There is a single X2 gene and it is found on chromosome 6 and there is a single C3 gene and it is on chromosome 3. The X2 mRNA is expressed in T cells and B cells and the C3 mRNA is expressed in T cells and neither X2 or C3 is expressed in monocytes or in neutrophils. Anti-sera have been raised against X2 and C3 and cell lines have been derived expressing the proteins. Studies to identify the natural ligands for X2 and C3 and to determine the roles for these receptors in lymphocyte physiology are ongoing.